- People are increasingly using rapid coronavirus tests to screen for the virus before attending an event.
- Rapid antigen tests for the new coronavirus are less accurate than the “gold standard” polymerase chain reaction (PCR) test, but antigen tests are cheaper and faster to run.
- Experts say the rise in rapid testing could give people a false sense of security.
Earlier this month, shortly before Ohio Gov. Mike DeWine met President Donald Trump at an airport in Cleveland, the governor tested positive for a rapid antigen test for the new coronavirus, SARS-CoV-2, which causes COVID-19 disease. . ,
Two follow-up tests, with a more accurate polymerase chain reaction, than PCR test, showed that the governor did not have the virus.
This kind of false positive with an antigen test is not an isolated incident.
Dozens of people who took a rapid SARS-CoV-2 test developed by biotech company Quidel at a clinic in Manchester, Vermont, in July were told they had the virus.
Subsequent PCR tests performed by the state Department of Health found that only 4 of the 65 were positive.
With people across the United States returning to work and school – and flying in and out of food – companies, corporations and universities are turning to rapid tests as a way to identify people who have the virus.
But no test is completely accurate, which means that some cases will be missed (false negatives) and some people will be told that they have the virus even though they have not (false positives).
This can create confusion, especially if people are not aware of what type of test they have done.
But some experts say widespread testing, even if less accurate, could still help contain the COVID-19 pandemic in the United States.
There are three types
- Genetic testing look for the RNA of the virus in a nasal or throat swab, or in saliva samples. The most common type is a polymerase chain reaction (PCR) test.
- Antigen tests look for specific egg whites on the surface of the virus.
- Antibody tests are blood tests that look for signs that a person has an infection with the virus and an immune response. These are not used to diagnose an active infection.
The Centers for Disease Control and Prevention (CDC) considers PCR testing to be the “gold standard” of SARS-CoV-2 testing. These tests are performed by laboratories at hospitals, universities, and public health agencies.
Some labs can process samples within 1 day, but sometimes it takes much longer – with people waiting a week or more to find out if they tested positive.
Antigen tests can be done faster – with results in just 15 minutes – using saliva as a nasal swab. Like PCR tests, antigen tests show if someone has an active infection.
Although antigen tests are faster and the number of tests performed can be easily scaled up, they have a high false-negative rate – with as many as half of negative results invalid.
The Vermont Department of Health counts a positive antigen test only as a positive case if it is confirmed with a PCR test. Other states have similar procedures.
But PCR tests are not always accurate. Some studies have found that up to 29 percent of these tests can give false negatives.
The accuracy of these tests – both PCR and antigen – varies widely based on the test and its manufacturer.
Other factors can also influence the results: how a nasal swab or saliva sample was collected, how the sample was transported, how a person performs the test (and if they are well trained), and the equipment they it is used.
The purpose of testing is to identify people who have an infection with SARS-CoV-2 so that they can prevent it from spreading to others.
But if people do not get their results for 2 weeks or longer, it does not matter how accurate the test is. They have already missed the opportunity to isolate themselves.
Laboratories can reduce backlogs to some extent by adding more equipment and techniques, or by automating procedures.
Some experts have also suggested
Dr. Alexis Nahama, senior vice president of diagnostics at biotech company Sorrento Therapeutics Inc. in San Diego, however, says that it is really difficult to overcome backlogs simply by increasing the number of PCR machines.
“To really run the test on a full scale, you need to be able to decentralize where the test is done,” he said. “That’s why you need the doctors ‘offices and the dentists’ offices to carry out the tests. You can even have minilabs that can run many of the tests at airports. ”
A simple, quick test that can be performed at schools, restaurants, airports and stadiums would enable these places to identify people who have an infection before entering. This would reduce the risk of transfer to public institutions.
Sorrento is working on marketing a rapid test developed by Dr. Zev Williams and his team at the Columbia University Fertility Center in New York City.
The test can detect the presence of the RNA of the new coronavirus in a saliva sample in just 30 minutes. If the test is positive, the color of the fluid in the tube changes to yellow.
Preliminary analysis shows that the test is very accurate, in the lines of a PCR test. But unlike PCR tests, which require special equipment, Soriva’s saliva test requires only a simple heating block.
“This test would be perfectly suitable for a doctor’s office, like a hotel before people check in, like the airport before people get on a plane,” said Dr. Mark Brunswick, senior vice president of regulation at Sorrento.
He adds that the company expects to submit an application for its saliva test to the Food and Drug Administration (FDA) by the end of next week.
Others agree on the need for decentralized testing.
Dr. Michael Mina, a professor of epidemiology at Harvard TH Chan School of Public Health in Boston, states that the United States has to test almost everyone in the country almost every day – which means we run tens of millions of tests every day.
For that to happen, the tests must be simple, inexpensive, and available everywhere.
But Bobby Brooke Herrera, PhD, co-founder and CEO of biotech company e25 Bio, told The Atlantic that because the FDA compares newly created coronavirus tests to the PCR test, companies that develop tests are focused on accuracy. the cost of speed and convenience.
E25 has developed a paper test strip that can detect SARS-CoV-2 infection within 15 minutes with a saliva sample. It has not yet been approved by the FDA.
Opening the door to less accurate testing for the general public does not mean that PCR completely shuts down. Hospitals and other places that need very accurate results will pass this type of test.
But for large-scale, daily testing could still work less accurately.
In an article on STAT News, Dr. Jeffrey L. Schnipper and Paul E. Sax, both professors of medicine at Harvard Medical School, explain the statistics on how less accurate tests can help reverse the pandemic – if the tests are done often enough.
“Even if the test is not perfect, it is much better than what we do now, which hardly anyone tests without symptoms,” she wrote, “in part due to concerns about test compliance.”
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